Many power electric circuits require the conversion of electric power from one form to another. For example, various types of converter circuits are used as energy stabilizing devices for an AC or DC load. Such converter circuits are typically based on the storage of electrical energy in a coil during one certain moment and which is transferred to a load during a moment after. The energy is stored as a magnetic field around the coil so that the actual energy transfer realized by the discharge of the coil comprises the conversion of magnetic energy to electrical energy.
In most converters, the build-up of magnetic energy through the coil and its subsequent discharge are two independent phases which are performed concurrently. That is to say, energy is first built-up around the coil as a magnetic field and, during a subsequent independent stage, the coil is connected to an external load so that the stored energy can discharge through the load, thereby supplying energy thereto.
U.S. Pat. No. 4,695.932 (Higashino) describes a circuit for storing energy delivered from an AC supply which comprises a DC capacitor and reversible chopper between an AC/DC reversible conversion circuit connected to the AC supply and a current supply circuit including a superconductive coil. This capacitor is connected intermittently to the superconductive coil in response to the action of the reversible converter, so that when connected it delivers energy to the superconductive coil or receives energy therefrom. The reversible chopper circuit controls in accordance with required values the magnitude of transfer of energy between the DC capacitor and the superconductive coil.
By such means, a DC capacitor is intermittently connected to the superconductive coil by the action of the reversible chopper circuit which controls the coil current flow, and thereby acts so that energy is delivered to, and released from, the superconductive coil. By such means, energy can be stored in a superconductive coil when demand is low and can be withdrawn from the coil when demand is high thereby reducing large fluctuations in demand and achieving a more stable output.
However, the charge and discharge pulses are applied to the coil concurrently and this means that the energy stored within the coil cannot be increased during discharge. Since the coil functions as an energy reservoir, this is not an efficient manner of the energy control. This is somewhat analogous to allowing a water tank to supply water only when there is no income of water and vice versa when obviously it would be preferable to allow charge and discharge to be effected simultaneously and independently.
However, no such implementation has been suggested in the prior art.